I am planning to insulate my 6" rigid SS liner,installed inside an exterior chimney 12"x12" clay flue liner. The idea is to improve draft as much as possible and I'm debating between using 1" insulation wrap or pouring in an insulation mix intended for this application. I want to maximize the insulation's total "R" value so that I get the best bang for my buck and labor. The problem is that I cannot find "R" value for any products on any websites for either the wrap or the mix. My guess is I would get better insulation by filling the entire void with mix. The best I can find is that most 1/2" wrap is listed to zero clearance, and most mix at 1" is listed for zero clearance. Filling the entire void would give me more insulation even if the wrap had twice the "R" value. Any thoughts out there or is everybody hibernating for the Summer??